Bicycle damper

ABSTRACT

A damper for a bicycle having a primary unit and a remote unit that, in some arrangements, is substantially entirely outside of the primary unit. The primary unit includes a damper tube, a spring chamber, and a piston rod that supports a main piston. The main piston is movable within the damper chamber of the primary unit. The main piston and the damper tube at least partially define a compression chamber. The remote unit comprises a remote fluid chamber and, in some arrangements, an inertial valve within the remote unit. The inertial valve is preferably responsive to terrain-induced forces and preferably not responsive to rider-induced forces when the shock absorber is assembled to the bicycle.

RELATED APPLICATIONS AND INCORPORATION BY REFERENCE

This application is a divisional of U.S. patent application Ser. No.12/197,171, filed Aug. 22, 2008, now U.S. Pat. No. 8,336,683, whichclaims the benefit of U.S. Provisional Patent Application Nos.61/054,091, filed May 16, 2008, and 61/051,894, filed May 9, 2008.

The entireties of U.S. patent application Ser. No. 12/197,171 and U.S.Provisional Patent Application Nos. 61/054,091 and 61/051,894 are herebyincorporated by reference herein and made a part of the presentspecification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to vehicle suspension systems.More specifically, the present invention relates to an improved shockabsorber system to be incorporated into the suspension system of abicycle.

2. Description of the Related Art

Bicycles intended for off-road use, i.e., mountain bikes, commonlyinclude a suspension assembly operably positioned between the rear wheelof the bicycle and the frame of the bicycle. The suspension assemblytypically includes a shock absorber configured to absorb forces impartedto the bicycle by bumps or other irregularities of the surface on whichthe bicycle is being ridden. However, an undesirable consequence ofincorporating a suspension assembly in a bicycle is the tendency for theshock absorber to absorb a portion of the power output of a rider of thebicycle. In some instances, i.e. when the rider is standing, theproportion of power absorbed by the shock absorber may be substantialand may drastically reduce the efficiency of the bicycle.

Vehicle shock absorbers utilize inertia valves to sense rapidaccelerations generated from a particular part of the vehicle. Inertiavalves are also used to change the rate of damping in the shock absorberdepending on the magnitude of the acceleration. As an example, theinertia valve assembly may be arranged to adjust the damping of the rearshock in accordance with accelerations that are generated by the body ofthe vehicle differently than it would adjust the damping of the rearshock for accelerations that are generated by the rear wheel of thevehicle.

One example of the type of shock absorber that utilizes an inertia valveto distinguish rider-induced forces from terrain-induced forces and isdescribed in U.S. Pat. No. 6,604,751 B2. According to U.S. Pat. No.6,604,751, the shock absorber of U.S. Pat. No. 6,604,751 is positionedbetween the swing arm and the main frame to provide resistance to thepivoting motion of the swing arm. The rear shock absorber includes aperipherally located fluid reservoir that is connected to the swing armat a distance away from the shock body, and is hydraulically connectedto the main shock body by a hydraulic hose. In one embodiment, thereservoir of U.S. Pat. No. 6,604,751 is connected to the swing armportion of the bicycle above the hub axis of the rear wheel.

The inertia valve assembly of U.S. Pat. No. 6,604,751 discloses aninertia valve attempting to overcome the effects of external forces andmanufacturing defects that inhibit the motion of the inertia valve withthe use of one or more “Bernoulli Steps” on an interior surface of theinertia mass. Also, the peripherally located reservoir of U.S. Pat. No.6,604,751 discloses a blowoff valve that allows for an increased flowrate after a minimum threshold pressure is exceeded inside the blowoffchamber. Typically, this will occur when the bicycle hits a severe bump.Further, the refill ports and the axial blowoff passages of the shockabsorber of U.S. Pat. No. 6,604,751 are located on the top surface ofthe reservoir.

However, the blowoff valve of U.S. Pat. No. 6,604,751 is not adjustable.That is, no mechanism is provided for adjusting the opening thresholdpressure of the blowoff valve. A rear shock absorber sold on the 2007model year and 2008 model year Epic bicycle sold by the assignee of thepresent application, Specialized Bicycle Components, Inc., includes amain shock body and a reservoir. An inertia valve mechanism and acompression valve mechanism are provided in the reservoir. Thecompression valve mechanism includes a one-way valve having one or moreshims that normally close one or more ports in a reservoir piston. Thecompression valve mechanism also includes a needle-and-orifice-typevalve, or bleed valve, which includes a needle member that is movablevia an external adjustment knob to vary an amount of fluid flow throughthe orifice. However, due to the location of the compression valvemechanism within the reservoir between the inertia valve and a floatingpiston, the adjustment rod that couples the needle member with theadjustment knob must pass through either the floating piston or theinertia mass. In the actual Epic shock absorber, the adjustment rodpasses through the floating piston, which increases the complexity ofmanufacturing and assembling the shock absorber. Thus, the need existsfor an improved rear inertia valve shock that provides advantageousadjustment features and is relatively easy and cost-effective tomanufacture.

SUMMARY OF THE INVENTION

A preferred embodiment is a bicycle rear shock absorber, including adamper tube having a first end portion, a second end portion and a sidewall extending between the first end portion and the second end portion.A piston rod carries a first piston. The first piston and the piston rodare capable of telescopic movement with respect to the damper tube. Thefirst piston cooperates with the damper tube to at least partiallydefine a variable volume compression chamber and the piston rod extendsout of the first end portion of the damper tube. A seal head creates aseal between the first end portion of the damper tube and the pistonrod. A remote reservoir tube has a first end portion, a second endportion and a side wall extending between the first end portion and thesecond end portion. The remote reservoir tube and the damper tube arenot within one another. At least a portion of the remote reservoir tubedefines a reservoir chamber. A fluid passage extends between thecompression chamber and the reservoir chamber. The damper tube defines afirst opening that permits fluid communication between the compressionchamber and the fluid passage and the remote reservoir tube defines asecond opening that permits fluid communication between the fluidpassage and the reservoir chamber. A compression damping circuit withinthe remote reservoir tube regulates compression fluid flow between thecompression chamber and the reservoir chamber. The compression dampingcircuit includes a pressure-activated valve including a partition and anacceleration-activated valve including an inertia mass. The partition isupstream from the inertia mass relative to a flow of compression fluidfrom the second opening to the reservoir chamber.

Another preferred embodiment is a bicycle rear shock absorber, includinga damper tube and a piston rod that carries a first piston. The firstpiston and the piston rod are capable of telescopic movement withrespect to the damper tube. The first piston cooperates with the dampertube to at least partially define a variable volume compression chamber.A reservoir tube has a first end portion, a second end portion and aside wall extending between the first end portion and the second endportion. A portion of an interior space of the reservoir tube defines areservoir chamber. A fluid passage extends between the compressionchamber of the damper tube and the reservoir tube, wherein the fluidpassage communicates with an opening into the reservoir tube. Acompression damping circuit within the reservoir tube regulatescompression fluid flow between the compression chamber and the reservoirchamber. The compression damping circuit comprises a pressure-activatedvalve including a partition and an acceleration-activated valveincluding an inertia mass. An externally-accessible adjustment mechanismpermits adjustment of the compression damping circuit. Both the openinginto the reservoir tube and the externally-accessible adjustmentmechanism are located at the first end portion of the reservoir tube.

Yet another preferred embodiment is a bicycle rear shock absorber,including a damper tube and a piston rod that carries a piston. Thepiston and the piston rod are capable of telescopic movement withrespect to the damper tube. The first piston cooperates with the dampertube to at least partially define a variable volume compression chamber.A reservoir tube has a first end portion, a second end portion and aside wall extending between the first end portion and the second endportion. A portion of an interior space of the reservoir tube defines areservoir chamber. A fluid passage extends between the compressionchamber of the damper tube and the reservoir tube. The fluid passagecommunicates with an opening into the reservoir tube. A compressiondamping circuit within the reservoir tube regulates compression fluidflow between the compression chamber and the reservoir chamber. Thecompression damping circuit comprises a pressure-activated valveincluding a first partition and an acceleration-activated valveincluding an inertia mass. A movable second partition within thereservoir tube separates the reservoir chamber from a gas chamber. Theinertia mass is located between the first partition and the movablesecond partition along an axis of the reservoir chamber.

Another preferred embodiment is a bicycle rear shock absorber, includinga damper tube and a piston rod that carries a piston. The piston and thepiston rod are capable of telescopic movement with respect to the dampertube. The piston cooperates with the damper tube to at least partiallydefine a variable volume compression chamber. A portion of an interiorspace of a reservoir tube defines a reservoir chamber. A fluid passageextends between the compression chamber of the damper tube and thereservoir chamber of the reservoir tube. A partition is provided withinthe reservoir tube. A shaft is provided within the reservoir tube. Aninertia mass is supported on the shaft and is movable relative to theshaft in response to an acceleration force above a threshold valueacting on the reservoir tube. A compression damping fluid circuit thatregulates compression fluid flow from the compression chamber to thereservoir chamber, includes a first compression damping flow path inwhich damping fluid passes through an acceleration-activated valve thatis controlled by a position of the inertia mass, a second compressiondamping flow path in which damping fluid passes through apressure-activated valve of the partition without passing through theshaft, and a third compression damping flow path in which damping fluidpasses through the shaft without passing through theacceleration-activated valve and without passing through thepressure-activated valve of the partition.

Another preferred embodiment is a bicycle rear shock absorber, includinga damper tube and a piston rod that carries a first piston. The firstpiston and the piston rod are capable of telescopic movement withrespect to the damper tube, wherein the first piston cooperates with thedamper tube to at least partially define a variable volume compressionchamber. A reservoir body has a first end portion, a second end portionand a side wall extending between the first end portion and the secondend portion. A portion of an interior space of the reservoir tubedefines a reservoir chamber. A fluid passage extends between thecompression chamber of the damper tube and the reservoir body. The fluidpassage communicates with an opening into the reservoir body. Anacceleration-activated damping circuit is within the reservoir body andincludes an inertia mass movable along an axis. A pressure-activateddamping circuit within the reservoir body regulates a compression fluidflow and a rebound fluid flow between the compression chamber and thereservoir chamber. The compression fluid flow within the reservoir bodyflows alongside the inertia mass and imparts a force on the inertia masstending to move the inertia mass in a first direction along the axis andthe rebound fluid flow within the reservoir body flows alongside theinertia mass and imparts a force on the inertia mass tending to move theinertia mass in a second direction along the axis.

Yet another preferred embodiment is a bicycle rear shock absorber,including a damper tube that defines a first diameter and a piston rodthat defines a second diameter. The piston rod carries a piston. Thepiston and the piston rod are capable of telescopic movement withrespect to the damper tube. The piston cooperates with the damper tubeto at least partially define a variable volume compression chamber andat least partially define a variable volume rebound chamber. A reservoirchamber is defined by the shock absorber. Fluid is displaced to thereservoir chamber from the compression chamber during compressionmovement of the shock absorber. Fluid returns to the compression chamberfrom the reservoir chamber during rebound movement of the shockabsorber. A ratio of the first diameter to the second diameter isbetween about 1.05:1 and about 1.75:1.

A preferred embodiment is a bicycle rear shock absorber, including adamper tube that defines a first diameter and a piston rod that definesa second diameter. The piston rod carries a piston. The piston and thepiston rod are capable of telescopic movement with respect to the dampertube. The piston cooperates with the damper tube to at least partiallydefine a variable volume compression chamber and at least partiallydefine a variable volume rebound chamber. A reservoir chamber is definedby the shock absorber, wherein fluid is displaced to the reservoirchamber from the compression chamber during compression movement of theshock absorber, and wherein fluid returns to the compression chamberfrom the reservoir chamber during rebound movement of the shockabsorber. The first diameter is between about 8 mm and about 12 mm-14 mmand a ratio of the first diameter to the second diameter is betweenabout 1.05:1 and about 2.5:1.

Another preferred embodiment is a bicycle rear shock absorber includinga main body portion. The main body portion includes a damper tube and apiston rod that carries a first piston. The first piston and the pistonrod are capable of telescopic movement with respect to the damper tube.A gas spring tube is capable of being coupled to the piston rod andwherein the gas spring tube is slidably engaged with an external surfaceof the damper tube. A reservoir body portion is not within the main bodyportion. A connector couples the damper tube and the reservoir bodyportion, wherein the connector is configured such that the gas springtube can be disconnected from the piston rod and slid along the dampertube until the gas spring tube at least partially overlaps the connectorwithout disassembling the connector from the damper tube or thereservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present bicycleshock absorber are described below with reference to drawings ofpreferred embodiments, which are intended to illustrate, but not tolimit, the present invention. The drawings contain fifteen (15) figures.

FIG. 1 is an elevation view of a bicycle including a preferred rearshock absorber, which includes an air spring and a damper.

FIG. 2 is a cross-section of the rear shock absorber of FIG. 1. Theshock absorber includes a main body portion and reservoir portion.

FIG. 3 is an enlarged cross-section of a main body portion of the shockabsorber of FIG. 2, showing a main body damping piston in anuncompressed position.

FIG. 4 is a cross-section of the main body damping piston taken alongline 4-4 of FIG. 3.

FIG. 5 is an enlarged cross-section of the main portion of the shockabsorber of FIG. 2, showing the main body damping piston in a partiallycompressed position.

FIG. 6 is an enlarged cross-section of the main portion of the shockabsorber of FIG. 2, showing the flow path of hydraulic fluid through themain body damping piston during the compression motion of the rearshock.

FIG. 7 is an enlarged cross-section of the main portion of the shockabsorber of FIG. 2, showing the flow path of hydraulic fluid through themain body damping piston during the rebound motion of the rear shock.

FIG. 8 is a cross-section of the reservoir of the shock absorber of FIG.1 showing an inertia valve in a closed position.

FIG. 9 is an enlarged cross-section of the reservoir of FIG. 8 showingthe inertia valve in a closed position.

FIG. 10 is a cross-section of a partition of the reservoir of FIG. 8taken along line 10-10 of FIG. 9.

FIG. 11 is an enlarged cross-section of the reservoir of FIG. 8 showingthe flow path of hydraulic fluid through the primary valve during thecompression motion of the rear shock, the inertia valve being in aclosed position.

FIG. 12 is an enlarged cross-section of the reservoir of FIG. 8 showingthe flow path of hydraulic fluid through the primary valve during therebound motion of the rear shock, the inertia valve being in a closedposition.

FIG. 13 is a cross-section of the reservoir of FIG. 8 showing theinertia valve in an open position.

FIG. 14 is an enlarged cross-section of the reservoir of FIG. 8 showingthe flow path of hydraulic fluid through the inertia valve during thecompression motion of the rear shock, the inertia valve accordinglybeing in an open position.

FIG. 15 is an elevation view of the shock absorber of FIG. 2 with theair sleeve in a partially disassembled state and moved along the dampertube toward the reservoir, which permits seal components of the airspring to be replaced without disassembly of the damper.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a bicycle 20 (e.g., a mountain bike) having apreferred embodiment of a rear suspension assembly including a rearsuspension element, or shock absorber, is illustrated. The bicycle 20includes a frame 22, preferably comprised of a generally triangular mainframe portion 24 and an articulating frame portion, or subframe 26,which preferably is pivotally connected to the main frame portion 24. Inthe illustrated arrangement, the subframe 26 is an assembly of multiplelinkage members pivotally connected to one another. The subframe 26 ispivotally connected to the main frame portion 24 (e.g., to the seat tube27). The bicycle 20 also includes a front wheel 28 and a rear wheel 30.The rear wheel 30 is carried by the subframe 26. A saddle or seat 32, toprovide support to a rider in a sitting position, is connected to themain frame 24 and, in particular, to the seat tube 27. In theillustrated arrangement, the seat 32 is connected to the main frame 24through a seat post 33. However, in other arrangements, the seat 32 maybe supported by another member or structure, such as the seat tube 27itself, for example. The front wheel 28 is supported relative to theframe 22 by a front suspension fork 34. It is understood that in someembodiments, main frame portion 24 may not be generally triangularand/or may not have a seat tube which extends uninterrupted to thebottom bracket.

Positioned between the subframe 26 and mainframe 24 (preferably, a toptube of the mainframe 24) is a preferred embodiment of a rear shock 38.It is noted that, while the shock 38 disclosed herein is described inthe context of its use as a rear shock absorber for an off-road bicycle,the applicability of the invention is not so limited. Aspects of theinvention can be utilized in a front suspension unit, such as thebicycle fork 34, and other suitable applications, as well.

The rear shock 38 influences the pivoting motion of the subframe 26,providing a suspension spring force and a damping force in bothcompression and rebound motion. Preferably, the spring is an air springarrangement, but coil springs and other suitable arrangements may alsobe used. Thus, the bicycle 20 illustrated in FIG. 1 includes the rearshock 38 operatively coupled between the rear wheel 30 and the frame 22.Advantageously, the rear shock 38 substantially reduces the transmissionof impact forces imparted on the rear wheel 30 by the terrain to theoperator of the bicycle.

With additional reference to FIG. 2, the rear shock 38 desirablyincludes a primary unit or main body portion 40 and a remote unit orsecondary or reservoir body portion 44. Note that, as illustrated, thereservoir body portion 44 may be located remote with respect to the mainbody portion 40. That is, the reservoir body portion 44 preferably isnot located within the main body portion 40. In the illustratedarrangement, the main body portion 40 and the reservoir portion arecoupled for fluid transfer via a tube assembly 46. As shown in FIG. 1,the main body portion 40 is coupled to the bicycle 20 separately fromthe reservoir body portion 44. The main body portion 40 preferablyextends from the main frame 24 (e.g., the top tube) at one end to thesubframe 26 (e.g., the seat stays) at the other end, and extendsunderneath the top tube, along the axis of the top tube. Preferably, thereservoir body portion 44 is connected to the bicycle 20 at a locationnear the rotational axis of the rear wheel 30. In the illustratedarrangement, the reservoir body portion 44 is coupled to one of the seatstays, near the rearward end portion thereof. Preferably, an upper endof the reservoir body portion 44 is coupled to the seat stay, and thereservoir body portion 44 extends below the seat stay. In theillustrated arrangement, an axis of the reservoir body portion 44 issubstantially perpendicular to the seat stay and generally vertical whenthe bicycle 20 is standing upright on a horizontal surface. However, inthe illustrated arrangement, the reservoir body portion 44 is notexactly vertical.

Preferably, the tube assembly 46 includes a tube portion 46 a and a hoseportion 46 b. The tube portion 46 a is constructed from a relativelyrigid material and generally defines an “S” shape, one end of which iscoupled to the main body portion 40 by a bayonet-type connection. Such aconnection securely couples the tube portion 46 a to the main bodyportion 40 in an axial direction of the connection, but permits relativerotation between the tube portion 46 a and the main body portion 40.Such an arrangement advantageously eases the assembly of the shockabsorber 38 to the bicycle 20 by permitting relative movement of themain body portion 40 and the tube assembly 46. In addition, the S-bendshape of the tube portion 46 a advantageously permits partialdisassembly of an air spring portion of the main body portion 40 forroutine servicing, without disassembly of the damper portion, as isdescribed in more detail below. The other end of the tube portion 46 ais coupled to a first end of the hose portion 46 b by any suitableconnector, such as a bayonet-type connector, for example. Preferably,the hose portion 46 b is constructed of a relatively flexible hose. Thesecond end of the hose portion 46 b is coupled to the reservoir bodyportion 44 by any suitable connector, such as a bayonet-type connector,for example. The flexible hose portion 46 b accommodates relativemovement between the main frame 24 and the subframe 26.

Although such an arrangement is presently preferred, in anotherarrangement, the reservoir body portion may be located within the mainbody portion, such as in a front fork, for example. In somearrangements, the reservoir body portion is directly connected to themain body portion external to the main body portion and, in otherarrangements, the reservoir body portion may be secured to the bicycleseparately, although relatively close to the main body portion. Forexample, the reservoir body portion may be coupled near the rear wheelaxle (or axis of rotation) and the main body portion may extend from themain frame 24 to a location near the rear wheel axis of rotation.Furthermore, the connection between the main body portion 40 and thereservoir body portion 44 can be achieved by any suitable means, such asby, but not limited to, threading or press-fitting the reservoir bodyportion 44 directly into the reservoir body portion 44 or the main bodyportion 40. Alternatively, the reservoir body portion 44 can bemonolithically formed with the main body portion 40.

As is discussed in more detail below, the shock absorber 38 preferablyincludes an inertia valve within the damping system of the shockabsorber 38. The inertia valve described herein may advantageously beconfigured to be highly responsive to changes in the acceleration of therear shock 38, or certain portions of the rear shock 38, such as thereservoir body portion 44, for example. Further, in some embodiments,the inertia valve components described herein are relativelyuncomplicated and cost-effective to produce, resulting in lowmanufacturing costs and few production errors. In particular, certainpreferred embodiments are configured to reduce assembly issuesassociated with tolerance stack-ups between the individual components,especially tolerance stack-ups in concentricity dimensions. Asdiscussed, the rear shock 38 preferably includes an inertia valve thatvaries the damping rate of the rear shock 38 depending upon thedirection of an acceleration of the inertia valve. With such anarrangement, the inertia valve can distinguish between forces impartedon the shock absorber 38 that originate from the rider of bicycle fromforces imparted on the shock absorber 38 by bumps in the path of travel.Performance of the bicycle is improved when forces generated by therider are more firmly (or quickly) damped and forces imparted on therear wheel 20 by bumps in the road are damped more softly (or slowly).This reduces or prevents shock absorber movement resulting fromrider-induced forces, such as by pedaling, while allowing the shockabsorber 38 to compensate for forces imparted on the rear wheel 20 byuneven terrain. It is understood that in some embodiments, the shockabsorber will move very little in response to rider induced pedalforces.

A preferred embodiment of the rear shock 38 is illustrated in FIGS.2-14. Generally, the rear shock 38 comprises a spring, a main damperassembly, and a reservoir. Preferably, the main body portion 40 isgenerally comprised of a hydraulic fluid body portion or damper tube 48,a spring tube or air sleeve 50 closed by a seal head or an end cap 52, amain body damping piston 54, and a damper tube cap or spring piston 56.

The damper tube 48 may be cylindrical in shape and includes an open endportion 58 and a lower closed end portion 60. The lower closed endportion 60 has a lower eyelet 62 that is used for connecting the shock38 to a portion of the bicycle 20 of FIG. 1, such as the subframeportion 26, for example. The closed end portion 60 or lower eyelet 62may be referred to herein as the “lower” end or eyelet as a matter ofconvenience because the end portion 60 coupled to the subframe 26 isoften relatively lower on the bicycle than the other end portion of theshock 38 coupled to the main frame 24. However, the term as used hereinis not intended to be limiting.

The air sleeve 50 may also be cylindrical in shape. The air sleeve 50includes an open end 64 and the opposite, upper end is closed by the endcap 52. The end cap 52 of the air sleeve 50 includes an upper eyelet 66that is used to connect the rear shock 38 to the seat tube 27 (or othersuitable portion) of the bicycle 20. The closed end portion 52 or eyelet66 may be referred to herein as the “upper” end or eyelet as a matter ofconvenience because the end portion 52 coupled to the main frame 24 isoften relatively higher on the bicycle than the other end portion of theshock 38 coupled to the subframe 26. However, the term as used herein isnot intended to be limiting.

The open end 64 of the air sleeve 50 slidingly receives the damper tube48. In this configuration, the air sleeve 50 and the damper tube 48 areconfigured for telescopic movement relative to one another between themain frame portion 24 and the subframe portion 26 of the bicycle 20.Thus, the shock absorber 38 is capable of varying in length toaccommodate relative movement of the main frame portion 24 and thesubframe portion 26 of the bicycle. Upward movement of the rear wheel 30(and subframe 26) tending to reduce the length of the shock 38 isusually referred to as compression movement or, simply, compression.Downward movement of the rear wheel 30 (and subframe 26) tending toincrease the length of the shock 38 is usually referred to as reboundmovement, or rebound, of the shock 38.

FIG. 1 illustrates an embodiment of the rear shock 38 mounted in itspreferred configuration to the main frame portion 24 (using upper eyelet66) and the subframe portion 26 (using lower eyelet 62) of the bicycle20. With reference to FIGS. 1 and 3, in the illustrated arrangement, themounting axes of the upper eyelet 66 and the lower eyelet 62,respectively, are not aligned. The mounting axis of the lower eyelet 62is rotated about the longitudinal axis of the shock 38 with respect tothe mounting axis of the upper eyelet 66 because, as illustrated in FIG.1, the subframe mounting tab 26 a is positioned at a differentorientation as compared to the mounting axis on the main frame portion24. However, while the orientation of the mounting axis of the lowereyelet 62 is not aligned or coplanar with the orientation of themounting axis of the upper eyelet 66 in the embodiment illustrated inFIGS. 1-3, the respective orientations of the eyelets 52, 58 is not solimited. The mounting axes of the eyelet 66, 58 can be positioned at anyrelative orientation suitable for the frame to which the rear shock 38is mounted.

In another embodiment, the orientation of the rear shock 38 may bechanged such that the damper tube 48 is attached to the seat tube 27 orother portion of the main frame 24 (at the “lower” eyelet 62) while theair sleeve 50 is attached to the subframe 26 (at the “upper” eyelet 66).However, such an arrangement is not presently preferred.

The air sleeve 50 has a seal assembly 68 positioned at the open end 64thereof, forming a substantially airtight seal between outer surface ofthe damper tube 48 and the inner surface of the air sleeve 50. Withreference to FIG. 3, in the illustrated embodiment, the seal assembly 68is comprised of an annular seal body 70 having a substantiallyrectangular cross-section that is located above, or inboard relative tothe open end 64, of an annular bearing 72. A wiper 74 is locatedadjacent the open end 64 of the air sleeve 50 to prevent dust, dirt,rocks, and other potentially damaging debris from entering into the airsleeve 50 as the damper tube 48 moves into the air sleeve 50.

The main damper piston 54 is positioned within and slides relative tothe inner surface of the damper tube 48. The piston 54 is connected tothe end cap 52 by a piston rod 78, fixing the piston 54 for motionwithin the air sleeve 50.

As described above, the damper tube cap 56 is fixed to the open endportion 58 of the damper tube 48. The damper tube cap 56 supports thepiston rod 78 such that the piston rod 78 is able to slide within acentral opening in the damper tube cap 56. Thus, the damper tube cap 56functions as a seal head of the damper tube 48. The damper tube cap 56accordingly slides within the inner surface of the air sleeve 50 and,thus, also functions as a piston of the air spring. Because the dampertube cap 56 is easier to manufacture in two portions, the damper tubecap 56 preferably is comprised of an upper cap portion 56 a and a lowercap portion 56 b (relative to the positions shown in FIG. 3). After thelower cap portion 56 b is inserted over the end of the damper tube 48,the upper cap portion 56 a is preferably fixed to the damper tube 48 bythreading the upper cap portion 56 a into threads formed on the insidesurface of the damper tube 48. The upper cap portion 56 a and lower capportion 56 b are configured such that, when the upper cap portion 56 ais attached to the damper tube 48 as described above, the lower capportion 56 b will also be firmly attached to the damper tube 48 andrelative axial movement therebetween is prevented. Annular seals 80 and82 are preferably used to prevent hydraulic oil from the damper tube 48from leaking into a primary air chamber 86 between the damper tube cap56 and the piston rod 78 and between the damper tube cap 56 and thedamper tube 48, respectively. Similarly, the annular seals 80, 82 alsoprevent the gas located in the primary air chamber 86 from leaking intothe damper tube 48.

A seal assembly 88 is preferably carried by the damper tube cap 56. Theseal assembly 88 is preferably comprised of a seal member 90, which ispreferably an annular seal having a substantially square cross-sectionand is positioned between a pair of bearings 92, and a bushing 94.Together, the seal member 90 and the bushing 94 create a seal betweenthe damper tube cap 56 and the air sleeve 50 and between the damper tubecap 56 and the piston rod 78, respectively, while allowing the pistonrod 78 to translate relative to the damper tube cap 56. Note that thecross-section of the seal member 90 may be any suitable shape, such asround or rectangular, for example.

A bottom-out bumper 96 is desirably positioned near the closed endportion 52 of the air sleeve 50 to prevent direct metal to metal contactbetween the closed end portion 52 and the damper tube cap 56 of thedamper tube 48 upon full compression of the rear shock 38. Thebottom-out bumper 96 is preferably formed from a soft, pliable, andresilient material, such as rubber. The bottom-out bumper 96 ispositioned between two washers 98 a, 98 b, which hold the bottom outbumper 96 in position next to the closed end portion 52. Washers 98 a,98 b can also be formed from a soft, pliable, and resilient material,such as rubber, or by any other suitable material. Similarly, an annularrebound (or top-out) bumper (not shown) may be positioned around theoutside of the damper tube 48 below the damper tube cap 56, but abovethe bearings 64. If provided, the rebound bumper preferably preventsmetal to metal contact between the bottom portion of the damper tube cap56 and the air sleeve 50, and buffers the magnitude of the impactbetween the two components, at the end of the rebound motion of the rearshock 38.

With particular reference to FIGS. 5 and 6, the space between the dampertube cap 56 and the seal assembly 68 defines a secondary air chamber102, which may be referred to as a “negative spring” chamber. Air thatfills the secondary air chamber 102 exerts a pressure that tends tocompress the shock 38 or resists the rebound motion of the rear shock38. In conjunction, the primary air chamber 86 and the secondary airchamber 102 form the suspension spring portion of the rear shock 38.

The primary air chamber 86 is defined as the space between the closedend portion 52 of the air sleeve 50 and the damper tube cap 56. Air heldwithin the primary air chamber 86 exerts a biasing force tending toextend the rear shock 38 or resist compression motion of the rear shock38. As will be appreciated, the primary air chamber 86 is primarilyresponsible for the spring characteristics of the shock 38 throughoutthe majority of the range of travel of the shock 38. The secondary airchamber 102 is intended to assist the initial compression of the shock38 to overcome the initial resistance to movement caused by, forexample, the various seal assemblies of the shock 38.

The damper assembly of the rear shock 38 is described hereinafter withreference to FIGS. 2-7. The interior space or chamber of the damper tube48 is divided by the piston 54 into two portions. In the illustratedarrangement, the first portion is the compression chamber 104 and thesecond portion is the rebound chamber 106. The compression chamber 104is generally formed by the space between the piston 54 and the closedend portion 60 of the damper tube 48. The compression chamber 104decreases in volume during compression motion of the rear shock 38 andincreases in volume during the rebound motion of the rear shock 38. Therebound chamber 106 is generally formed by the space between the piston54 and the damper tube cap 56. The rebound chamber 106 increases involume during the compression motion of the rear shock 38 and decreasesin volume during the rebound motion of the rear shock 38. In addition,the piston rod 78 is present within the rebound chamber 106. As thepiston 54 moves further into the damper tube 48, the piston rod 78occupies an increased portion of the interior of the damper tube 48.Thus, the rebound chamber 106 does not increase by the same volume asthe compression chamber 104 decreases during compression, due to thepresence of the piston rod 78 within the rebound chamber 106. As aresult, damping fluid must be displaced to the reservoir body portion 44upon compression and then replaced to the main body portion 40 duringrebound. As noted above, FIG. 3 illustrates an embodiment of the rearshock 38 wherein the piston 54 is in an uncompressed state. FIGS. 5, 6and 7 illustrate a partially compressed position of the rear shock 38.

As shown in FIG. 3, preferably, a hollow threaded fastener or pin 108fixes the piston 54 to the piston rod 78. A seal 110, preferably of anannular type having a rectangular cross-section, is carried by thepiston 54 and seals the piston 54 with the inner surface of the dampertube 48.

In the illustrated embodiment, the piston 54 preferably includes aplurality of compression flow passages 112. Each of the compression flowpassages 112 pass through the piston 54 in the axial direction and,preferably, circular in cross-sectional shape. In one preferredarrangement, nine compression flow passages 112 are provided in threegroups of three passages 112, as shown in FIG. 4. Alternatively, eachgroup of compression passages 112 could comprise a single, arcuate (orkidney-shaped) passage. However, the presently illustrated arrangementadvantageously provides for a similar amount of fluid flow, whilepermitting the passages 112 to be formed by a simple drilling operation,rather than a more time consuming and expensive milling operation, whichwould be required for an arcuate passage.

In various embodiments, the compression flow passages 112 maycumulatively perforate and, hence, allow the passage of hydraulic fluidthrough 10% to 60%, 15% to 40%, or 20% to 35% of the working area of thepiston 54. As used herein, “working area” means the area defined withinthe periphery of the piston 54 in a plane perpendicular to thelongitudinal axis. In the illustrated arrangement, the working areasubstantially corresponds to a cross-sectional area of the interiorspace of the damper tube 48. In the case of the piston 54, thelongitudinal axis is aligned with the piston rod 78. The compressionflow passages 112 may cumulatively perforate and allow the passage ofhydraulic fluid through at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%,50%, 55% and 60% of the working area.

The compression flow passages 112 are covered on the rebound chamber 106side of the piston 54 by a shim stack 114. The shim stack 114 can bemade up of one or more flexible, preferably annular, shims. The shimstack 114 preferably operates as a one-way check valve. That is, theshim(s) 114 deflect to allow a flow path of preferably minimalrestriction through the compression flow passages 112 during compressionmotion of the rear shock 38, while preventing flow through thecompression flow passages 112 during the rebound motion of the rearshock 38. In the illustrated configuration, the shim stack 114 is madeup of multiple shims having any suitable characteristics (e.g.,thicknesses, stiffnesses, and diameters) that preferably allow the shimstack 114 to be easily deflected to allow hydraulic fluid to flow withminimal restriction through compression flow passages 112 duringcompression motion of the rear shock 38. In addition, the relativelylarge collective area of the passages 112, which results in a relativelylarge fluid force acting on the shim stack 114, also assists in allowingflow with minimal restriction. The substantially unrestricted flow pathof hydraulic fluid (represented by arrows) through the compression flowpassages 112 and the deflection of the shim stack 114 during thecompression motion of the rear shock 38 are illustrated in FIG. 6.

In addition to the compression flow through the compression flowpassages 112, compression flow preferably is also permitted at leastthrough an additional compression flow path. For example, in theillustrated arrangement, the piston rod 78 defines a central passage 116therethrough. The central passage 116 is in communication with thecompression chamber 104 through a passage 118 of the hollow pin 108.Further, the central passage 116 is in communication with the reboundchamber 106 through a radial port 120 in the piston rod 78. FIG. 8 alsoillustrates the flow of hydraulic fluid from the compression chamber104, through the port 120 in the piston rod 78, into the rebound chamber106. For this flow path, the hydraulic fluid flows from the compressionchamber 104 through the hollow pin 108 and a central passage 116 of thepiston rod 78 before flowing out of the port 120 and into the reboundchamber 106. This flow path may be referred to as a pressure-activatedflow path because fluid flow through the flow path will occur inresponse to a pressure differential between the compression chamber 104and the rebound chamber 106.

The piston 54 of the illustrated embodiment also comprises a pluralityof rebound flow passages 122, preferably three, extending in the axialdirection through the piston 54. Each of the rebound flow passages 122preferably includes an axial throughhole portion 122 a and a radialchannel portion 122 b. The radial channel portions 122 b are formed onthe rebound side of the piston 54 and permit fluid to bypass thecompression shim stack 114 during the rebound motion of the rear shock38. As such, the hydraulic oil flows through both the radial channels122 b and the axial throughholes 122 a during the rebound motion of therear shock 38. A notable advantage of this configuration is that thesize of the compression flow passages 112 can be increased to permit avery high flow rate of hydraulic fluid through the piston 54 during thecompression motion without otherwise limiting the size of the reboundflow passages 122 and, hence, the amount of fluid that can flow throughthe rebound flow passages 122 that may otherwise be required if theradial channels 122 b were not present. This also permits the piston 54to be formed from a single piece of material, instead of a multi-pieceor cup design.

In certain embodiments, the rebound flow passages 122 may cumulativelyperforate and, hence, allow the passage of hydraulic fluid through 2% to25%, 5% to 15%, or 5% to 10% of the working area of the piston 54. Therebound flow passages 122 may cumulatively perforate and, hence, allowthe passage of hydraulic fluid through no more than 2%, 5%, 10%, 15%, or25% of the working cross-sectional area of the piston 54.

A rebound shim stack 124, which can be made up of one or more flexibleshims, preferably is positioned on the compression side of the piston 54and covers the rebound passages 122. The rebound shim stack 124 deflectsto allow, but to control the amount of, flow through the rebound flowpassages 122 during the rebound motion of the rear shock 38. As such,the rebound shim stack 124 provides resistance to the flow of hydraulicfluid through the piston 54 during the rebound motion of the rear shock38. The rebound shim stack 124 also prevents flow through the reboundflow passages 122 during the compression motion of the rear shock 38,but is preferably configured not to obstruct the flow of hydraulic oilthrough the compression flow passages 112 during compression motion. Forexample, in the illustrated arrangement, the piston 54 includes recesses126 on the compression chamber 104 side that incorporate the openings ofthe compression flow passages 112. The recesses 126 permit compressionflow through the compression flow passages 112 from the compressionchamber 104 even when the rebound shim stack 124 is closed.

FIG. 7 illustrates the flow path of hydraulic fluid (represented byarrows) from the rebound chamber 106, through the rebound flow passages122, to the compression chamber 104 during the rebound motion of therear shock 38. In addition, FIG. 7 illustrates the deflection of theshim stack 124, which permits flow through the rebound passages 122during the rebound motion of the rear shock 38.

FIG. 7 also illustrates the flow of hydraulic fluid from the reboundchamber 106, through the port 120, the central passage 116 of the pistonrod 78, and the passage 118 of the hollow pin 108 into the compressionchamber 104 during rebound motion of the rear shock 38. The port 120through the piston rod 78 provides a passage through which hydraulicfluid may flow between the central passage 116 and the rebound chamber106 when the rear shock 38 is partially to fully compressed. When therear shock 38 is in its substantially uncompressed position, asillustrated in FIG. 3, the bushing 94 blocks the port 120 tosubstantially prevent the hydraulic fluid from flowing through the port120 into the rebound chamber 106 or central passage 116. However, insome arrangements, the port 120 may be positioned or otherwiseconfigured such that fluid flow is permitted through the port 120 evenwhen the rear shock 38 is in the uncompressed position.

In the illustrated arrangement, an adjustment mechanism is provided thatpermits the flow rate through the port 120 to be varied or adjusted. Forexample, an adjustment rod 128 extends through the central passage 116of the piston rod 78. The adjustment rod 128 preferably is configured toalter the damping force in the rear shock 38 by altering the amount offluid that can flow through the port 120 upon compression motion andrebound motion. This is achieved by adjusting the adjustment rod 128such that a needle portion or tip 130 of the adjustment rod 128partially or, in some cases, fully blocks a valve seat portion 132 ofthe passage 118 of the hollow pin 108, thus restricting or, in somearrangements, fully preventing fluid from flowing through the port 120.The tip 130 and valve seat 132 include corresponding tapered surfacesand, thus, function as a needle-and-orifice-type adjustable valve.However, other suitable types of valves may be used in addition or inthe alternative.

Furthermore, because in the configuration of the main body portion 40illustrated in FIGS. 2-7, the compression flow passages 112 allowsignificantly more flow volume therethrough as compared to the reboundflow passages 122, adjustments to the volume of fluid that is permittedto flow through port 120 more significantly affects the rebound motionthan the compression motion of the rear shock 38. Thus, while adjustmentof the adjustment rod 128 alters fluid flow from the compression chamber104 to the rebound chamber 106 during both compression motion andrebound motion, the adjustment rod 128 more significantly adjusts thefluid flow from the compression chamber 104 to the rebound chamber 106during the rebound motion of the rear shock 38. The rebound damping, ascompared to the compression damping, is more greatly affected by theadjustment of the adjustment rod 128 for the following reason. For thesake of example, ignoring the flow restriction provided by the variousshim stacks, the compression flow passages 112 are desirably configuredto allow a greater flow rate therethrough as compared to the reboundflow passages 122. This is because, as discussed above, the cumulativesize of the openings comprising the compression flow passages 112 isdesirably significantly greater than the cumulative size of the openingscomprising the rebound flow passages 122. Further, the size of theopening comprising the port 120 is preferably much less than thecumulative size of the openings comprising the compression flow passages112. In certain embodiments, the size of the opening comprising the port120 can be 2% to 30%, 5% to 25%, or 10% to 20% of the cumulativecross-sectional area of the openings comprising the compression flowpassages 112. In certain embodiments, the size of the opening comprisingthe port 120 is no more than 30%, 25%, 15%, 10%, or 5% of the cumulativecross-sectional area of the openings comprising the compression flowpassages 112. Thus, the additional flow through the port 120 does notsignificantly increase the flow from the compression chamber 104 to therebound chamber 106 during the compression motion of the rear shock 38.

Similarly, the size of the opening comprising the port 120 is preferablyless than the cumulative cross-sectional area of the openings comprisingthe rebound flow passages 122. In certain embodiments, thecross-sectional area of the opening comprising the port 120 can beapproximately 15% to approximately 35% of the cumulative cross-sectionalarea of the openings comprising the rebound flow passages 122. Incertain embodiments, the cross-sectional area of the opening comprisingthe port 120 is no more than 25% of the cumulative cross-sectional areaof the openings comprising the rebound flow passages 122. In sum,because the ratio of the size of the port 120 to the size of theopenings comprising the rebound flow passages 122 is greater than theratio of the size of the port 120 to the size of the openings comprisingthe compression flow passages 112, allowing flow through the port 120will more significantly affect the net overall flow during the reboundmotion of the rear shock 38 as compared to the compression motion of therear shock 38. Therefore, adjustments to the adjustment rod 128 willpreferably have a greater effect on rebound damping as compared tocompression damping of the rear shock 38.

As such, the adjustment rod 128 provides the user of the rear shock 38with the ability to adjust the rebound damping of the rear shock 38. Anadjustment knob 134, which is attached to the end of the reboundadjustment rod 128, allows a user to adjust the adjustment rod 128 and,hence, the rebound damping rate of the rear shock 38. The adjustmentknob 134 is located on the outside of the rear shock 38. Thus, it iseasily and externally accessible by the user to allow for dampingadjustments without requiring disassembly of the rear shock 38. A balldetent mechanism 136 provides a plurality of distinct adjustmentpositions of the adjustment knob 134. It is noted that the tip 130 ofthe adjustment rod 128 may or may not completely prevent flow throughthe port 120 in the fully closed, or downward-most, position. That is, afluid-tight seal may not be created between the tip 130 of theadjustment rod 128 and the valve seat 132 even in the fully closedposition. Thus, some fluid may flow through the port 120 in its “closed”position. Such fluid flow is often referred to as “bleed flow” and,preferably, is limited to a relatively small flow rate. Some amount ofbleed flow may be intentionally permitted, or may result from normalmanufacturing variations in the sizes or shapes of the tip 130 and valveseat 132. A seal member, such as an O-ring 138, inhibits or preventsfluid from moving beyond the tip 130 portion of the adjustment rod 128and into an upper portion of the central passage 116.

As described above, the rear shock 38 also includes a reservoir bodyportion 44 that is coupled to the main body portion 40. The interiorchamber of the reservoir body portion 44 communicates with thecompression chamber 104 through a passage 140 a that extends through theclosed end portion 60 of the damper tube 48 of the main body portion 40.This permits hydraulic fluid to move between the reservoir body portion44 and the compression chamber 104. In a rear shock 38 such as thatillustrated herein, in which the piston rod 78 occupies a varying volumeof the interior of the damper tube 48 as the shock 38 compresses andextends, damping fluid moves from the main body portion 40 to thereservoir body portion 44 to accommodate the increasing volume of thepiston rod 78 within the damper tube 48 during compression and movesfrom the reservoir body portion 44 to the main body portion 40 toreplace the increased volume within the damper tube 48 caused by theevacuation of the piston rod 78 from the damper tube 48 during rebound.Thus, the reservoir body portion 44 acts as a reservoir, or accumulator,for the damping fluid within the rear shock 38.

With reference to FIGS. 2 and 8-14, the reservoir body portion 44includes a reservoir tube 142. The reservoir tube 142 is closed on bothends thereof. A partition, such as a floating reservoir piston 144, ispositioned inside of the reservoir tube 142 and divides the interiorspace of the reservoir tube 142 is divided into a reservoir chamber 146and a gas chamber 148. In the illustrated arrangement, the floatingreservoir piston 144 is in sealed, sliding engagement with an insidesurface of the reservoir tube 142. A substantially fluid-tight sealbetween the interior surface of the reservoir tube 142 and the reservoirpiston 144 is provided by a seal member 150. Although other suitableseals may also be used, the seal member 150 is preferably asubstantially round cross-section, annular seal. Although a floatingpiston 144 is presently preferred due to the relatively simpleconstruction and reliable performance, other types of partitions may beused, such as a bladder arrangement, for example. In addition, acompressible member, such as a closed-cell foam member, may bepositioned in the reservoir tube 142 and configured to collapse toenlarge the size of the reservoir chamber 146 and to expand to reducethe size of the reservoir to accept damping fluid from the main body 40and return (or encourage the return of) damping fluid to the main body40, respectively.

An end cap 152 closes the reservoir chamber 146 portion of the reservoirtube 142. In the illustrated arrangement, the end cap 152 is located atan upper end of the reservoir tube 142. As discussed above, the tubeassembly 46 is attached to the end cap 152 and allows the reservoir bodyportion 44 to interface with the closed end portion 60 of the dampertube 48 so that hydraulic fluid can flow from the passage 140 in theclosed end portion 60 of the damper tube 48 to the reservoir chamber 146of the reservoir body portion 44. In particular, preferably, the end cap152 defines a fluid passage 153 that permits fluid to be transferredbetween the tube assembly 46 and the interior of the reservoir tube 142.

A second end cap 154 closes the gas chamber 148 end of the reservoirtube 142, which in the illustrated arrangement is lower end of thereservoir tube 142 (both in FIG. 8 and as assembled to the bicycle 20).The cap 154 includes a valve assembly 156 to add or remove gas, such asnitrogen, for example, to or from the gas chamber 148. The positivepressure exerted on the floating reservoir piston 144 by the pressurizedgas within the gas chamber 148 causes the floating reservoir piston 144to exert a pressure on the hydraulic fluid in the reservoir chamber 146.With such an arrangement, the positive pressure causes the gas chamber148 to expand to include any space made available when hydraulic fluidflows from the reservoir chamber into the compression chamber. It alsoimproves the flow of fluid from the reservoir body portion 44 into thecompression chamber 104 during the rebound motion of the rear shock 38.

A pressure-activated valve assembly and an inertia-activated (oracceleration-activated) valve assembly are positioned within thereservoir body portion 44. The inertia valve assembly 160 includes aninertia mass 162 slidably supported by a reservoir shaft 164. Theinertia mass 162 is lightly biased to a closed position by a biasingmember, such as a spring 166. In the illustrated arrangement, the closedposition is upward relative to an open position of the inertia mass 162.When in the open configuration, the inertia valve assembly 160 permitscommunication between the reservoir chamber 146 and the compressionchamber 104. Stated another way, when the inertia valve assembly 160 isin the open configuration, hydraulic fluid is permitted to flow from thecompression chamber 104 through the passage 140 and an internal passage168 of the reservoir shaft 164, and out through reservoir shaft fluidports 170 into the reservoir chamber 146.

Preferably, the pressure-activated valve assembly includes a primaryvalve assembly 172 and a two-way or bleed valve assembly 174. Theprimary valve assembly 172 is positioned above the inertia valveassembly 160, or upstream of the inertia valve assembly 160 relative toa compression fluid flow direction within the reservoir body portion 44.The primary valve assembly 172 includes a piston or partition 180 thatis fixed within the reservoir tube 142 and defines a partition betweenthe reservoir chamber 146 and an upper portion of the interior of thereservoir tube 142 that communicates with the compression chamber 104(referred to herein as the primary valve chamber 182). In theillustrated arrangement, the partition 180 is carried by the end cap 152and, preferably, includes external threads that engage with internalthreads of the end cap 152. The partition includes a centrally-locatedopening, which supports the reservoir shaft 164. In the illustratedarrangement, the opening includes internal threads that mate withexternal threads of the reservoir shaft 164. A shoulder portion 184 isdefined where the reservoir shaft 164 reduces in diameter. The shoulder184 supports an annular washer 186. The annular washer 186 supports acompression flow shim stack 188 of the primary valve assembly 172against a lower face of the piston 180. The washer 186 also defines anupper stop for the inertia mass 162 to define a closed position of theinertia mass 162.

As illustrated, the partition 180 has one or more axial compression flowpassages 190 and one or more axial refill ports 192. The compressionflow shim stack 188 regulates the flow rate of hydraulic fluid throughthe compression flow passages 190. In one embodiment, between 50 lbs and75 lbs of force is required to be exerted on the compression flow shimstack 188 in order to deflect the compression flow shim stack 188 enoughto allow the hydraulic fluid to flow through the compression flowpassages 190 at a rate that allows the piston 54 to move within thedamper tube 48 at a rate of approximately 0.05 m/s. In anotherembodiment, between 25 lbs and 50 lbs of force is required to be exertedon the compression flow shim stack 188 in order to allow the piston 54to move within the damper tube 48 at a rate of approximately 0.05 m/s.

In certain embodiments, when there is at least about 25 lbs, 35 lbs, 45lbs, 55 lbs, 65 lbs or 75 lbs of force exerted on the compression flowshim stack 188, the shim stack 188 deflects thereby opening the dampingvalve. Specifically, the compression flow shim stack 188 deflects enoughto allow the piston 54 to move within the damper tube 48 at a rate ofapproximately 0.05 meters/sec.

However, to regulate the flow rate of hydraulic fluid through thecompression flow passages 190, a flow element having a series of portsmay be substituted for the shim stack 188. In general, any of the shimstacks described herein may be replaced or augmented with a flow elementhaving a series of ports for the purpose of regulating the flow rate ofhydraulic fluid through the various components comprising the rear shock38. In addition, other suitable arrangements may also be used. Forexample, a check plate (with or without a biasing member), an elastomermember, or other suitable methods for controlling damping fluid flowthrough a passage may also be used.

The axial compression flow passages 190 may cumulatively perforate and,hence, allow the passage of hydraulic fluid through, 10% to 50%, or 25%to 35%, of the working surface area of the partition 180, which may bedefined as the area bounded by a peripheral edge of the partition 180.In the illustrated arrangement, the working area substantiallycorresponds to a cross-sectional area of the interior space of thereservoir tube 142. The axial refill ports 192 may cumulativelyperforate and, hence, allow the passage of hydraulic fluid through, 10%to 50% or more of the working surface area of the partition 180. Theaxial refill ports 192 may cumulatively perforate and allow the passageof hydraulic fluid through 2% to 25% of the working surface area of thepartition 180. The axial refill ports 192 may cumulatively perforate andallow the passage of hydraulic fluid through the partition 180 at a flowrate approximately equal to the amount of flow of hydraulic fluid thatis flowing through passage 140, i.e., approximately equal to the amountof flow of hydraulic fluid that is flowing from the reservoir bodyportion 44 to the main body portion 40.

In one embodiment, the compression flow shim stack 188 is configured todeflect to allow, but damp the flow rate of, hydraulic fluid through thecompression flow passages 190 at normal operating pressures of the rearshock 38. In certain embodiments, each of the shims comprising thecompression flow shim stack 188 is preferably a bendable disc made froma metallic alloy. In one embodiment, five shims that are approximately16 mm in diameter and 0.15 mm thick, stacked together, would produce acompression damping force of approximately 75-80 lbs at a rate of fluidflow that allows the piston 54 to move within the damper tube 48 at arate of approximately 0.05 m/s. In another embodiment, four shims thatare approximately 16 mm in diameter and 0.15 mm thick, stacked together,would produce a compression damping force of approximately 65-70 lbs ata rate of fluid flow that allows the piston 54 to move within the dampertube 48 at a rate of approximately 0.05 m/s. In another embodiment,three shims that are approximately 16 mm in diameter and 0.15 mm thick,stacked together, would produce a compression damping force ofapproximately 55-60 lbs at a rate of fluid flow that allows the piston54 to move within the damper tube 48 at a rate of approximately 0.05m/s. In another embodiment, two shims that are approximately 16 mm indiameter and 0.15 mm thick, stacked together, would produce acompression damping force of approximately 45-50 lbs at a rate of fluidflow that allows the piston 54 to move within the damper tube 48 at arate of approximately 0.05 m/s, and so on. In another embodiment, threeshims having approximately a 21 mm OD, an 8 mm ID and a 0.24 mmthickness are positioned on an approximately 0.7 mm dished piston andpinched on an approximately 12 mm OD pivot shim generating approximately250-300 pounds of force at shaft speeds between approximately 1 in/s and10 in/s. Shim stack configurations that include a lesser or greaternumber of shims and that produce less damping force or greater dampingforce than recited above may also be used.

The compression flow shim stack 188 of the present invention operates todamp the compression motion of the rear shock 38 and, accordingly, canbe configured to deflect to allow hydraulic fluid to flow through thecompression flow passages 190 at low or regular operating pressureswithin the primary valve chamber 182. In one embodiment, approximately90% or more of the compression motion damping of the rear shock isaccomplished by the compression flow shim stack 188 located in thereservoir body portion 44, whereas the remainder of the compressionmotion damping of the rear shock is accomplished by other components ofthe rear shock (e.g., the compression shim stack 114 located in the mainbody portion 40). In another embodiment, approximately 80% or more ofthe compression motion damping of the rear shock is accomplished by thecompression flow shim stack 188 located in the reservoir body portion44. In yet another embodiment, approximately 70% or more of thecompression motion damping of the rear shock is accomplished by thecompression flow shim stack 188 located in the reservoir body portion44. In yet another embodiment, approximately 50% or more of thecompression motion damping of the rear shock is accomplished by thecompression flow shim stack 188 located in the reservoir body portion44.

As described above, the pressure-activated valve assembly also includesa two-way valve, or bleed valve 174, which selectively permits fluidflow between the primary valve chamber 182 and the reservoir chamber 146in both the compression and rebound directions. The bleed valve 174 maybe referred to as a pressure-activated valve (as opposed to anacceleration-activated valve, for example) because the valve 174 isresponsive to pressure differentials between the primary valve chamber182 and the reservoir chamber 146. In the illustrated arrangement, thebleed valve 174 is a needle-and-orifice-type valve. In particular,preferably, an adjustment rod 194 extends downwardly from the end cap152. An upper end of the adjustment rod 194 includes external threadsthat mate with interior threads of a central opening of the end cap 152.The reservoir adjustment rod 194 preferably is in rotationalcommunication with an adjustment rod driver 196, which is supported forrelative rotation by the end cap 152. An adjustment knob 198 is coupledfor rotation with the driver 196. The adjustment knob 134 is locatedexternally of the reservoir tube 142 such that a user can access theadjustment knob 134 without disassembly of the shock 38. The adjustmentrod 194 and the driver 196 are configured such that rotational motion istransmitted therebetween, but such that translational motion ispermitted, such as by a splined connection, for example. Thus, rotationof the driver 196 (via rotation of the knob 134) causes rotation of theadjustment rod 194. As a result of the threaded engagement between theadjustment rod 194 and the end cap 152, rotation of the adjustment rod194 results in simultaneous translation, or axial movement, of theadjustment rod 194 relative to the end cap 152, which allows the fluidflow through the bleed valve 174 to be adjusted, as described below. Aball detent mechanism 136 located between the knob 134 and end cap 152provides distinct adjustment positions of the adjustment knob 134.

Further, the adjustment rod 194 includes a tip portion 194 a thatpreferably adjustably regulates the flow of hydraulic fluid through ametering rod flow port 202 located within the reservoir shaft 164. Thetip 194 a preferably defines a tapered surface that tapers to a smallercross-sectional diameter toward the bottom end of the tip 194 a (i.e.,the end closest to the port 202). The largest diameter of the conicalportion preferably is greater than the diameter of the cylindricalmetering rod flow port 202, and the smallest diameter of the conicalportion preferably is smaller than the diameter of the cylindricalmetering rod flow port 202. With such an arrangement, the flow ofhydraulic oil through the metering rod flow port 202 can be reduced byadvancing the tip 194 a of the adjustment rod 194 into the metering rodflow port 202. In some arrangements, the flow of hydraulic oil throughthe metering rod flow port 202 can be substantially prevented by fullyengaging the tip 194 a of the bleed valve plug 182 with the metering rodflow port 202. However, some amount of flow may occur through aclearance space between the tip 194 a and the metering rod flow port202, which may occur by design or due to normal manufacturing variationsin the size or shape of the tip 194 a and the port 202, possibly amongother components.

Advantageously, the overall structure of the illustrated reservoir bodyportion 44 facilitates the provision of damping adjustment features inshock absorber 38 that can be manufactured in a cost-effective manner.For example, preferably, the partition 180 is provided on the same endportion of the reservoir tube 142 in which the damping fluid isdelivered from the main body portion 40 (via the passage 153). Thus,externally-accessible adjustment features (e.g., the adjustment rod 194and associated components) may be incorporated without addingunnecessary complexity. For example, in the illustrated arrangement,because the adjustment rod 194 extends from the same end of thereservoir body portion 44 from which the damping fluid is delivered tothe reservoir body portion 44, the damping fluid is easily accessibleand the adjustment rod does not need to be excessively long. Inparticular, it is advantageous that the adjustment rod 194 enters thereservoir body portion 44 on the reservoir chamber 146 side of thefloating piston 144 and, thus, does not need to extend through thefloating piston 144. In an arrangement in which an adjustment rod needsto pass through the floating piston, it is necessary to provide a sealbetween the adjustment rod and floating piston, which increases thefrictional drag on the floating piston. Moreover, the dimensionaltolerances (especially concentricity dimensions) must be tightlycontrolled to allow assembly and smooth operation of the components overa reasonable lifespan. Such tightly controlled tolerances increase thecost of manufacturing the shock absorber. In addition to the adjustmentrod 194, which permits adjustment of the bleed valve 174, the primaryvalve 172 and/or inertia valve 160 are conveniently accessible from theend of the reservoir body portion 44 into which the damping fluid isdelivered from the main body portion 40 such that additionalexternally-accessible adjustment mechanisms could be provided, such asby being incorporated into the end cap 152, for example.

As described above, the partition 180 also includes refill ports 192,which permit rebound fluid flow through the partition 180. A reboundflow shim stack 204 covers the refill ports 192 on an upper face of thepartition 180. In the illustrated embodiment, the rebound flow shimstack 204 is comprised of a single shim that preferably is biased to aclosed position by a biasing mechanism, such as a spring. Thus, as usedherein, a “shim stack” may include one shim or multiple shims. In theillustrated embodiment, the biasing mechanism is at least one andpreferably multiple wave washers 206 positioned between the shim 204 andthe end cap 152. Preferably, the wave washers 206 lightly bias the shim204 to the closed position, but permit the shim 204 to open in responseto a relatively small opening force. In the illustrated arrangement,four wave washers 206 are provided, with a single flat washer 208interposed between the wave washers 206 and the shim 204. Thus, therebound flow shim 204 substantially prevents fluid from flowing from theprimary valve chamber 182 to the reservoir chamber 146 through refillports 192, while not significantly inhibiting fluid flow from thereservoir chamber 146 into the primary valve chamber 182 through therefill ports 192. Although preferred, the rebound flow shim stack 204 isnot limited to the illustrated arrangement. The rebound flow shim stack204 can be comprised of multiple shims, similar to the compression flowshim stack 188 described above.

In the illustrated embodiment, the damping control of the rebound motionof the rear shock 38 is advantageously at least primarily located in themain shock body of the rear shock 38, as opposed to being located in thereservoir body portion 44. Because the rebound flow restriction, orrebound damping, is primarily located in the main shock body of the rearshock 38, the flow of hydraulic fluid into the compression chamber 104is not disturbed by cavitation or other flow disrupting effects that canresult when the hydraulic fluid is sucked or pulled through the flowrestriction devices or shim stacks that are located in the reservoirs ofother, conventional designs. In the illustrated embodiment, during therebound motion of the rear shock, a compressive force pushes thehydraulic fluid located in the rebound chamber 106 through the reboundflow passages 122, thus avoiding cavitation and other flow efficiencyeffects that may otherwise result. Another benefit of having thecompression damping primarily occur in the reservoir body portion 44 andthe rebound damping primarily occur in the main body portion 40 is thatthe heat generated by each is transferred to separate portions of thedamping fluid within the overall system.

In certain embodiments, at least 90%, at least 80%, at least 70%, atleast 60% or at least 50% of the rebound motion damping of the rearshock 38 is accomplished in the main body portion 40, whereas theremainder of the rebound damping of the rear shock is accomplished byother components of the rear shock (preferably in the reservoir bodyportion 44). In one embodiment, this rebound damping in the main bodyportion 40 can be substantially accomplished by the rebound shim stack124 located in the main body portion 40.

FIG. 12 illustrates the flow of hydraulic fluid from the reservoirchamber 146, through the rebound flow passages 192 and port 202, as wellas the corresponding preferred deflection of the rebound flow shim stack204, when the inertia valve 160 is in the closed position. As shown,preferably, the rebound flow travels along a side of the inertia mass162 along an axis of motion and in a closing direction of the inertiamass 162. Thus, advantageously, the rebound fluid flow can exert a fluidforce on the inertia mass 162 tending to close it more quickly when theshock 38 changes from compression motion to rebound motion.

As described previously, the inertia valve assembly 160 is positionedwithin the reservoir tube 142 and includes the inertia mass 162 slidablysupported on the reservoir shaft 164. As illustrated in FIGS. 13 and 14,the plurality of radially extending reservoir shaft fluid ports 170,each preferably having a generally cylindrical geometry, extend radiallythrough the reservoir shaft 164. The reservoir shaft fluid ports 170connect the passage 168 to the reservoir chamber 146. The inertia mass162 is normally biased to an upward position by a biasing mechanism,such as the spring 166, to normally close the ports 170. The spring 166is supported by a stop 210 that is secured to a lower end of thereservoir shaft 164, such as by a threaded connection or other suitablearrangement. In response to a suitable acceleration force, the inertiamass 162 slides in a downward direction relative to the reservoir shaft164 to open the ports 170, as is discussed in greater detail below.

The diameter of each reservoir shaft fluid port 170 may be between 0.5mm and 5.0 mm. As illustrated, the reservoir shaft 164 preferably has atotal of six equally spaced reservoir shaft fluid ports 170, each with adiameter equal to approximately 1.0 mm. In another embodiment, thediameter of each reservoir shaft fluid port 170 is approximately 1.5 mmor more. In another embodiment, the diameter of each reservoir shaftfluid port 170 is approximately 2.0 mm or more. In another embodiment,the diameter of each reservoir shaft fluid port 170 is approximately 3.0mm or more. In yet another embodiment, the diameter of each reservoirshaft fluid port 170 is approximately 4.0 mm or more. In anotherembodiment, the diameter of each reservoir shaft fluid port 170 isapproximately 5.0 mm or more. In another embodiment, the reservoir shaft164 may have two, four or more reservoir shaft fluid ports 170,regardless of the diameter of the reservoir shaft fluid ports 170. Incertain embodiments, the total cross-sectional area of the reservoirshaft fluid ports 170 is 2 square millimeters to 100 square millimeters,2 square millimeters to 80 square millimeters, 2 square millimeters to60 square millimeters, 2 square millimeters to 40 square millimeters, 2square millimeters to 20 square millimeters, 2 square millimeters to 10square millimeters, or 2 square millimeters to 5 square millimeters. Incertain embodiments, the total cross-sectional area of the reservoirshaft fluid ports 170 is no more than 12 square millimeters, no morethan 10 square millimeters, no more than 8 square millimeters, no morethan 6 square millimeters, or no more than 5 square millimeters.

Furthermore, in one embodiment, when an upward acceleration force isapplied to the reservoir body portion 44 of the rear shock 38 (such aswhen the bicycle 20 encounters a bump) that causes the inertia valve 160to open and causes the piston 54 to move within the damper tube 48 at arate of approximately 1.0 m/s, the components comprising the inertiavalve 160 will preferably be configured such that virtually all of thehydraulic fluid flows into the reservoir chamber 146 via the reservoirshaft fluid ports 170 and, accordingly, such that only a small volume ofhydraulic fluid, if any, flows through the compression flow passages 190at that rate of piston 54 movement. However, the inertia valve 160 ofthat same embodiment will preferably be configured such that, when therear shock 38 encounters a more severe bump that causes the piston 54 tomove within the damper tube 48 at a rate of approximately 4.0 m/s, thecomponents comprising the inertia valve 160 will preferably beconfigured such that approximately 20% or more of the total flow ofhydraulic fluid flowing into the reservoir chamber 146 will flow throughthe reservoir shaft fluid ports 170 and approximately 80% or less of thetotal flow of hydraulic fluid flowing into the reservoir chamber 146will flow through the compression flow passages 190.

In certain embodiments, when the rear shock 38 encounters a more severebump that causes the piston 54 to move at a rate of approximately 4.0m/s, the components comprising the inertia valve 160 will preferably beconfigured such that at least 80%, at least 70%, at least 60%, at least50%, at least 40%, or at least 35% of the total flow of hydraulic fluidflowing into the reservoir chamber 146 will flow through passages otherthan passages closable by the inertia mass 162 (e.g., in the illustratedembodiment, the compression flow passages 190 and the bleed valve port202).

In certain embodiments, the inertia valve 160 will preferably beconfigured such that, when the rear shock 38 encounters a more severebump that causes the piston 54 to move at a rate of approximately 4.0m/s, the components comprising the inertia valve 160 will preferably beconfigured such that no more than 10%, no more than 20%, no more than30%, no more than 40%, no more than 50% or no more than 60% of the totalflow of hydraulic fluid flowing into the reservoir chamber 146 will flowthrough the passages closable by the inertia mass (e.g., in theillustrated embodiment, the reservoir shaft fluid ports 170).

The inertia mass 162 preferably is made from a relatively densematerial, for example a dense metal such as brass, and preferably has amass less than approximately two ounces. In another embodiment, theinertia mass 162 preferably has a mass less than approximately one andone-half ounces. In another embodiment, the inertia mass 162 has aweight of approximately 32 grams, or 1.13 ounces. In another embodiment,the inertia mass 162 preferably has a mass less than approximately oneounce. In yet another embodiment, the inertia mass 162 preferably has amass less than or equal to approximately one-half ounce. The inertiamass 162 preferably is relatively free of any axial passages or othersophisticated internal features or contours other than the main,cylindrical passage through the longitudinal center of the inertia mass162, and also the annular groove 212 on the inside surface of theinertia mass 162. Without such passages and sophisticated internalfeatures and contours, the inertia mass 162 is advantageously easier tomanufacture, does not require substantial deburring on the internalsurfaces, and is less likely to bind or stick to the reservoir shaft 164as compared to other, conventional designs. The annular groove 212 ispreferably formed on the inside surface of the inertia mass 162 to limitthe amount of surface area on the inside surface of the inertia mass 162that may come into contact with the outer surface of the reservoir shaft164 and, hence, limit the amount of drag between the two components.Preferably, the inertia mass 162 has a streamlined geometricconfiguration such that the mass to fluid resistance ratio is increased.In addition, the lower end of the inertia mass 162 includes a recess 214that accommodates an upper end of the biasing spring 166 and defines aspring seat that is contacted by one end of the biasing spring 166. Inthe illustrated arrangement, the inertia mass 162 includes one or more,and preferably a pair, of axial ports 216 that pass radially through theinertia mass 162 and open into the recess 214. The ports 216 may assistin evacuating fluid from between the inertia mass 162 and the stop 210as the inertia mass 162 moves downward such that movement of the stop210 is not inhibited. In some embodiments, the inertia mass 162 may alsohave an annular groove (not shown) around the exterior of the inertiamass 162.

As discussed previously, the spring 166 biases the inertia mass 162 intoan upward, or closed, position wherein the inertia mass 162 covers theopenings of the reservoir shaft fluid ports 170 to substantially preventfluid flow from the passage 168 to the reservoir chamber 146.Preferably, when the inertia mass 162 is in a closed (upward) position,flow to the reservoir chamber 146 primarily occurs through thecompression flow passages 190 in the partition 180. FIG. 11 illustratesthe flow of hydraulic fluid from the passage 168 through the compressionflow passages 190 in the partition 180 and into the reservoir chamber146, as well as the corresponding preferred deflection of thecompression flow shim stack 188, when the inertia valve 160 is in theclosed position. However, the flow path, but not necessarily the flowvolume, of hydraulic fluid through the compression flow passages 190 inthe partition 180 and into the reservoir chamber 146 may be asillustrated in FIG. 11 even if the inertia valve 160 were in an openposition.

As discussed, the inertia mass 162 is also movable into a downward, oropen, position against the biasing force of the spring 166. In the openposition, which is illustrated in FIGS. 13 and 14, the inertia mass 162uncovers at least a portion of the reservoir shaft fluid ports 170 toallow fluid to flow therethrough, and a reduced compression damping rateis achieved. The stop 210 preferably operates as the lowermost stopsurface for the inertia mass 162. With the illustrated arrangement,preferably, hydraulic fluid flows from the passage 168 through thereservoir shaft fluid ports 170, and around and along the inertia mass162 into the reservoir chamber 146. Note that, while the inertia mass162 is in the open position, hydraulic fluid may still flow from thepassage 168 through the compression flow passages 190 in the partition180 and into the reservoir chamber 146, as illustrated in FIG. 11, inaddition to flowing through inertia valve.

It is noted that, while the inertia mass 162 may be described as havingan open and a closed position, the inertia mass 162 likely does notcompletely prevent flow through the reservoir shaft fluid ports 170 inthe closed position. That is, a fluid-tight seal is not typicallycreated between the inertia mass 162 and the reservoir shaft 164 onwhich it slides. Thus, some fluid may flow through the inertia valve 160in its closed position. Such fluid flow is often referred to as “bleedflow” and, preferably, is limited to a relatively small flow rate. Tocreate a fluid-tight seal between the inertia mass 162 and the reservoirshaft 164 would require precise dimensional tolerances, which would beexpensive to manufacture, and may also inhibit movement of the inertiamass 162 on the reservoir shaft 164 in response to relatively smallacceleration forces.

With reference to FIGS. 9-12, another advantageous feature of theillustrated inertia valve 160 is a circumferential groove 218 around theexterior of the reservoir shaft 164. The center plane of the groove 218preferably aligns with the axial centerlines of each of the reservoirshaft fluid ports 170. The groove 218 functions as a flow accumulator,equalizing the pressure of the hydraulic fluid emanating from thereservoir shaft fluid ports 170.

The groove 218 preferably may comprise an upper chamfer portion, anarcuate portion, and a lower chamfer portion. The width of the groove218 (i.e., the combined width of the upper chamfer portion, the arcuateportion, and the lower chamfer portion) is preferably greater than thediameter of each of the reservoir shaft fluid ports 170 such the groove218 extends both above and below each of the reservoir shaft fluid ports170 and such that a significant amount of fluid can accumulate in thegroove 218. In another embodiment, the groove 218 could be smaller thanthe diameter of the ports 170. The groove 218 allows the fluid pressureto be distributed evenly over the inner circumference of the inertiamass 162. The even distribution of fluid pressure preferably creates aforce tending to center the inertia mass 162 around the reservoir shaft164, thus partially or fully compensating for any inconsistencies influid pressure that would otherwise occur due to the locations ororientations of, or variations in size between, the individual reservoirshaft fluid ports 170. Such a feature helps to prevent binding of theinertia mass 162 on the reservoir shaft 164. The prevention of bindingof the inertia mass 162 on the reservoir shaft 164 is beneficial in abicycle application because it is desirable that the inertia valve bevery sensitive to any terrain features which may only transmitrelatively small acceleration forces to the inertia valve 160.

The preferred configuration of the groove 218 provides a nearly uniform(i.e., simultaneous) cutoff of hydraulic fluid flow emanating from eachof the reservoir shaft fluid ports 170 as the inertia mass 162 revertsto its closed position. This is beneficial to ensuring that the inertiamass is not pushed off-center by the reservoir shaft fluid ports 170. Asdiscussed, the preferred configuration of the groove 218 alsoadvantageously ensures that the inertia mass 162 is not pushedoff-center by a non-uniform flow of hydraulic fluid through thereservoir shaft fluid ports 170, or by non-uniform forces exerted by thehydraulic fluid flowing through the reservoir shaft fluid ports 170,during the compression motion of the rear shock 38.

Additionally, the chamfers may advantageously provide for a progressiveshut off of hydraulic fluid flow through the reservoir shaft fluid ports170 as the inertia mass 162 reverts to its closed position. Inparticular, as the acceleration causing the inertia mass 162 to movedownward relative to the reservoir shaft fluid ports 170 is reduced,causing the inertia mass 162 to move upward, the inertia mass 162 firstblocks the flow of hydraulic fluid flowing away from the lower chamferportion, thus blocking only a portion of the hydraulic fluid flow goingthrough the reservoir shaft fluid ports 170 in this position. Thehydraulic fluid flowing from the lowest portion of the lower chamferportion is less than the hydraulic fluid flowing from the upper portionof the lower chamfer portion. Thus, as the hydraulic mass 162 continuesto move upward, it progressively blocks a greater amount of thehydraulic fluid flowing away from the lower chamfer portion. As thehydraulic mass 162 continues to move upward, it progressively blocks agreater portion of the arcuate portion and, finally, the upper chamferportion, until substantially all of the hydraulic fluid flowing throughthe reservoir shaft fluid ports 170 is stopped.

Although the illustrated reservoir body portion 44 includes an inertiavalve 160, in other arrangements, the inertia valve 160 may be omittedor may be replaced with, or supplemented with, other compression orrebound fluid flow valves. However, the inertia valve 160 is preferredbecause it operates to distinguish terrain-induced forces fromrider-induced forces. Terrain-induced forces are generally upwardlydirected (compression) forces caused by the vehicle (such as a bicycle)encountering a bump. Rider-induced forces, in the case of a bicycleapplication, typically are short duration, relatively large amplitudeforces generated from the pedaling action or other aggressive movementsof the rider. The inertia valve may alternatively be configured tooperate in response to rebound forces, rather than compression forces.

The illustrated embodiment includes multiple features that enhance theperformance, durability, longevity adjustability and manufacturability,among other features, aspects and advantages of the shock absorber 38.For example, the direction of fluid flow within the reservoir chamber146 tends to pass alongside the inertia mass 162 in both compression andrebound motion of the shock absorber 38. In addition, the flow tends tobe generally aligned with the axis of movement of the inertia mass 162.Thus, advantageously, the flow of fluid within the reservoir chamber 146tends to assist in opening the inertia mass 162 during compression andassist in closing the inertia mass 162 during rebound. Accordingly, inaddition to the features described above, such an arrangement furtherenhances the sensitivity of the inertia valve 160 in comparison toarrangements in which the flow is isolated from the inertia mass in oneor both of compression and rebound movement.

In addition, as discussed above, the compression damping attributes ofthe shock absorber 38 preferably are primarily influenced by thecompression damping valves (e.g., primary valve assembly 172 and bleedvalve assembly 174) within the reservoir body portion 44. Accordingly,the larger the volume of damping fluid displaced from the main bodyportion 40 to the reservoir body portion 44, the greater the possibilityfor manipulating the flow of damping fluid to create the desired dampingeffect. For example, a greater volume of damping fluid introduced intothe reservoir body portion 44 (or wherever the primary damping valvesare located) allows for more separate damping circuits to be utilizedand/or allows for more adjustable damping valves to be provided.

Advantageously, the damper components (e.g., damper tube 48 and pistonrod 78) of the illustrated main body portion 40 are configured such thatthe main damper functions substantially as a pump during compression ofthe shock absorber 38. That is, the damper components of the main bodyportion 40 are configured to move a large portion of the total availablefluid volume of the damper tube 48 from the main body portion 40 to thereservoir body portion 44 during compression. In the illustratedarrangement, such pumping action is achieved primarily by providing alarge outside diameter piston rod 78 relative to the inside diameter ofthe reservoir tube 48. Accordingly, the piston rod 78 tends to displacea significant volume of the total fluid within the damper tube 48 to thereservoir body portion 44 during a complete compression stroke. Theparticular percentage of the fluid displaced can be calculated for anyof the possible combinations of component or shock absorber 38dimensions or characteristics as described immediately below. Forexample, a total volume of the damper tube 48, total volume of thepiston rod 78 and, thus, the displacement percentage could be calculatedor reasonably estimated based on, for example, each of the possibleshock lengths, piston rod 78 diameters, reservoir tube 48 diameters,clearances or ratio's, described below. Preferably, at least about 30%of the damping fluid within the damper tube 48 is displaced by thepiston rod 78 during a complete compression stroke. In somearrangements, at least about 40, 45, 50, 60, 70 80 or 90% of the dampingfluid within the damper tube 48 is displaced by the piston rod 78 duringa complete compression stroke. In one presently preferred arrangement,approximately 46% of the damping fluid within the damper tube 48 isdisplaced by the piston rod 78 during a complete compression stroke.Displacement of a significant percentage of the total fluid within thedamper tube 48 could also be accomplished by not allowing any fluid flowthrough the main body damping piston 54 (i.e., a piston displacementarrangement). However, preferably, as discussed above, fluid flow ispermitted through the main body damping piston 54 during compression tobe used during subsequent rebound motion of the shock absorber 38.Piston displacement arrangements require some method of filling therebound chamber, which would be difficult to accomplish in an integratedrear shock absorber arrangement (i.e., both spring and dampingfunctions) while maintaining a reasonable manufacturing cost and weight.In addition, with the illustrated arrangement, the main body portion 40and reservoir body portion 44 may be described as having a master/slaverelationship. For example, during compression motion, the damping actionof the shock absorber 38 preferably is primarily controlled by thecompression damping circuit(s) within the reservoir body portion 44.Thus, the reservoir body portion 44 is the master to the main bodyportion 40 slave because the reservoir body portion 44 controls themotion and the main body portion 40 moves as permitted by the dampingaction within the reservoir body portion 44. On rebound, the roles maybe reversed. For example, the rebound damping preferably is controlledprimarily by the rebound damping circuit(s) of the main body portion 40,which acts as the master to control rebound fluid flow. The flow withinthe rebound circuit(s) of the reservoir body portion 44 is controlled bythe main body portion 40 rebound damping circuit(s) and, thus, acts asthe slave to the rebound damping circuit(s) of the main body portion 40.

In a preferred arrangement, in the context of a bicycle rear shockabsorber 38, the piston rod outer diameter is between about 6 mm andabout 20 mm and, more preferably, between about 8 mm and about 20 mm.However, the piston rod outer diameter may be about 9 mm, 10 mm, 11 mm,12 mm, 13 mm, 14 mm, 15 mm 16 mm, 17 mm, 18 mm or 19 mm. In oneparticularly preferred arrangement, the piston rod outer diameter isabout 12 mm. Furthermore, in other arrangements, taking into accountother factors or applications, the piston rod outer diameter may belarger or smaller than the above-described dimensions. In a preferredarrangement, the damper tube inner diameter is between about 8.4 mm andabout 35 mm. More preferably, the damper tube inner diameter is betweenabout 14 mm and about 21 mm. A presently preferred embodiment of thedamper tube inner diameter is about 17.7 mm. However, the damper tubeinner diameter may be about 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15mm 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, 22 mm, 23 mm, 24 mm, 25 mm,26 mm, 27 mm, 28 mm, 29 mm, 30 mm, 31 mm, 32 mm, 33 mm or 34 mm,preferably taking into account the outer diameter of the piston rod 78and providing a desirable amount of clearance between the two toaccommodate an appropriate sealing arrangement. Preferably, the minimumdiametrical clearance totals at least about 1.5 mm (i.e., about 0.75 mmof radial clearance). In a preferred arrangement, the clearance totalsbetween about 1.5 mm and about 9.5 mm. More preferably, the totalclearance is between about 1.5 mm and about 8 mm. However, the totalclearance may be about 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm or 9 mm,among other possibilities depending on the size, application or otherrelevant factors of the shock absorber 38.

In a preferred arrangement, a ratio of the damper tube 48 insidediameter to the piston rod 78 outside diameter is between about 1.05:1and about 1.75:1. In a presently preferred arrangement the ratio isabout 1.5:1 and, more specifically, about 1.48:1. However the ratio maybe about 1.05:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, or1.75:1. With a shock absorber 38 having a piston rod outer diameter anddamper tube inner diameter sized substantially within the rangesdescribed above (preferably, a piston rod outer diameter between about6-20 mm and a damper tube inner diameter of about 8-35 mm and, morespecifically, with a piston rod outer diameter of about 12 mm and adamper tube inner diameter of about 17.7 mm and/or within about anycombination of the length, travel and leverage ratio ranges discussedbelow), the ratio of the damper tube 48 inside diameter to the pistonrod 78 outside diameter may be as much as about 2.0:1 or about 2.5:1.

A preferred shock absorber 38 has a length (usually measured between thecenters of the eyelets 62 and 66) of between about 6.5 and about 10.25inches and, more preferably, between about 6.5 and about 9.5 inches. Aparticularly preferred embodiment has a length of about 7.36 inches. Thetotal travel of the shock absorber 38 preferably is between about 1 andabout 5 inches, between about 1 and about 4 inches, or between about 1and about 3.5 inches. A particularly preferred embodiment of the shockabsorber 38 has a total travel of about 47 mm (or about 1.85 inches). Aparticularly preferred embodiment of the shock absorber 38 has aleverage ratio when installed on a bicycle of about 4:1 and, morespecifically, about 3.98:1. The leverage ratio is the ratio of thetravel of the wheel axis compared to the travel of the shock absorber.Thus, the wheel tends to travel about 4 times as far as the shock travelon average throughout the complete travel range of the wheel. However,the leverage ratio may vary at any particular portion of the full rangeof travel.

The operation of the rear shock 38 is discussed with reference to FIGS.1-14. As discussed above, the rear shock 38 preferably is operablymounted between movable portions of the bicycle frame 22, such asbetween the main frame 24 (e.g., the seat tube 27) and the subframeportion 26 of the bicycle 20. Preferably, the damper tube 48 portion ofthe rear shock 38 is connected to the subframe portion 26 and the airsleeve 50 (and, thus, the piston rod 78 and piston 54) is connected tothe seat tube 27. As shown in FIG. 1, the reservoir body portion 44 ispreferably connected to the subframe portion 26 of the bicycle 20 nearthe rear axle. The rear shock 38 is capable of both compression andrebound motion.

When the rear wheel 30 of the bicycle 20 is impacted by a bump, thesubframe portion 26 rotates with respect to the main frame portion 24,tending to compress the rear shock 38. The inertia mass 162 is biased bythe force of the spring 166 to remain in the closed position. In orderfor the inertia mass 162 to overcome the force of the spring 166 andmove to an open position such that fluid flows from the passage 168through the reservoir shaft fluid ports 170 and into the reservoirchamber 146, the acceleration experienced by the reservoir body portion44 along its longitudinal axis must exceed a threshold value.

For compression motion of the rear shock 38 (i.e., for the piston 54 tomove into the damper tube 48), the fluid that is displaced by the pistonrod 78 must flow into the reservoir chamber 146. However, when theinertia mass 162 is in a closed position with respect to the reservoirshaft fluid ports 170, fluid flow into the reservoir chamber 146preferably is substantially impeded. When the inertia valve 160 is inthe closed position, the rear shock 38 preferably remains substantiallyrigid. As noted above, some amount of fluid flow from the compressionchamber 104 to the reservoir chamber 146 preferably is permitted throughthe bleed valve 174. However, preferably, the fluid flow through thebleed valve 174 is restricted to a level such that the bleed valve 174is primarily effective for permitting settling or sag of the shock 38over a (relatively short) period of time. The flow through the bleedvalve 174 preferably is insufficient to permit the shock 38 to beresponsive to bumps in response to fluid flow solely through the bleedvalve 174.

However, even if the inertia valve 160 remains in the closed position,fluid can still transfer from the compression chamber 104 into thereservoir chamber 146 if the compressive force exerted on the rear shock38 is of a magnitude sufficient to increase the fluid pressure withinthe primary valve chamber 182 to a pressure threshold level that willcause the compression flow shim stack 188 to open and allow fluid toflow from the primary valve chamber 182 through the compression flowpassages 190 and into the reservoir chamber 146.

In the configurations described herein, the positive or extension springforce of the rear shock 38 is produced by the pressure of the gas in theprimary air chamber 86. The damping rate in compression is determinedmainly by the flow through the compression flow passages 190 in thereservoir body portion 44, as well as the less significant dampingeffects produced by the compression shim stack 114 in the main bodyportion 40.

If a sufficient magnitude of acceleration is imposed along thelongitudinal axis of the reservoir body portion 44 (i.e., the axis oftravel of the inertia mass 162), the inertia mass 162 will overcome thebiasing force of the spring 166 and move downward relative to thereservoir shaft 164 into an open position. With the inertia valve 160 inthe open position, hydraulic fluid is able to be displaced from thecompression chamber 104 through the reservoir shaft fluid ports 170 andinto the reservoir chamber 146. Thus, the rear shock 38 is able to becompressed and the compression damping preferably is determinedprimarily by flow through the compression flow passages 190 in thereservoir body portion 44, as well as the reservoir shaft fluid ports170.

The mass of the inertia mass 162, the spring rate of the spring 166, andthe preload on the spring 166 determine the minimum threshold for theinertia mass 162 to overcome the biasing force of the spring 166 andmove to the open position. The spring rate of the spring 166 and thepreload on the spring 166 are preferably selected such that the inertiamass 162 is biased by the spring 166 into a closed position when noupward acceleration is imparted in the axial direction of the reservoirbody portion 44. However, the inertia mass 162 will preferably overcomethe biasing force of the spring 166 when subject to an acceleration thatis between 0.1 and 3 times the force of gravity (G's). Preferably, theinertia mass 162 will overcome the biasing force of the spring 166 uponexperiencing an acceleration that is between 0.25 and 1.5 G's. However,the predetermined threshold may be varied from the values recited above.

With reference to FIGS. 13 and 14, when the inertia mass 162 is in theopen position, the spring 166 exerts a biasing force on the inertia mass162 which tends to move the inertia mass 162 toward the closed position.Advantageously, with the exception of the spring biasing force and fluidresistance, the inertia mass 162 moves freely within the body of fluidcontained in the reservoir chamber 146 to increase the responsiveness ofthe inertia valve 160 and, hence, the rear shock 38 to forces exerted onthe rear wheel 30. The inertia valve 160 differentiates between bumpysurface conditions and smooth surface conditions, and alters the dampingrate accordingly. During smooth surface conditions, the inertia valve160 remains in a closed position and the damping rate is desirably firm,thereby inhibiting suspension motion due to the movement of the rider ofthe bicycle 20. When the first significant bump is encountered, theinertia valve 160 opens to advantageously lower the damping rate so thatthe bump may be absorbed by the rear shock 38.

Once the rear shock 38 has been compressed, either by fluid flow throughthe primary valve assembly 172 or the inertia valve 160, or both, thespring force generated by the combination of the primary air chamber 86and the second air chamber 102 tends to bias the damper tube 48 awayfrom the air sleeve 50. In order for the rear shock 38 to rebound, avolume of fluid equal to the volume of the piston rod 78 exiting thereservoir tube 142 must be drawn from the reservoir chamber 146 and intothe compression chamber 104. Fluid flow is allowed in this directionthrough the refill ports 192 in the primary valve assembly 172 against adesirably light resistance offered by the rebound flow shim stack 204.Gas pressure within the gas chamber 148 exerting a force on the floatingreservoir piston 144 may assist in this refill flow. Thus, the rebounddamping rate is determined primarily by fluid flow through the reboundflow passages 122 of the primary piston 54 against the biasing force ofthe rebound shim stack 124.

As discussed, the present rear shock 38 includes an inertia valve 160comprising an inertia mass 162 and a reservoir shaft 164 having acircumferential groove 218 in the reservoir shaft 164 aligned with thereservoir shaft fluid ports 170 to create an even distribution of fluidpressure on the inertia mass 162 and, hence, substantially inhibit orprevent the inertia mass 162 from binding on the reservoir shaft 164.The off-center condition of the inertia mass 162 may cause it to contactthe reservoir shaft 164 causing friction, which tends to impede motionof the inertia mass 162 on the reservoir shaft 164. Due to therelatively small mass of the inertia mass 162 and the desirability ofhaving the inertia mass 162 respond to small accelerations, any frictionbetween the inertia mass 162 and the reservoir shaft 164 seriouslyimpairs the performance of the inertia valve 160 and may render itentirely inoperable. The off-center condition may result from typicalvariations associated with the manufacturing processes needed to producethe components of the inertia valve 160. Further, the binding effect ofthe inertia mass 162 may result from burrs located on the inner surfaceof the inertia mass 162 or the outer surface of the reservoir shaft 164.Because the inertia mass 162 advantageously has a generally smooth innersurface, the deburring operations on the inside surface of the inertiamass 162 are substantially simplified and the risk of binding issubstantially reduced.

With reference to FIGS. 2 and 15, preferably, the shock absorber 38 isconfigured to permit at least partial disassembly of the suspensionspring portion without disassembly of the damper portion. Thus, routineservicing of the suspension spring is made possible, withoutnecessitating draining of the damping fluid from the damper.Accordingly, the routine servicing of the suspension spring is much moreconvenient. The servicing of the suspension spring usually involvesreplacement and/or lubrication of one or more seals (e.g., seal 90, seal70) of the suspension spring. However, access to the interior of the airsleeve 50 for any purpose is enhanced.

In the illustrated arrangement, the air sleeve 50 can be uncoupled fromthe end cap 52 and slid towards the closed end 60 of the damper tube 48.The tube assembly 46 is configured such that the air sleeve 50 can passover the tube portion 46 a of the tube assembly 46 a sufficient distanceto permit servicing of the air spring. As illustrated, preferably, thetube portion 46 a exits the damper tube 48 at less than a 90 degreeangle relative to a longitudinal axis of the damper tube 48. Morepreferably, the tube portion 46 a exits the damper tube 48 at less than75 degrees, less than 60 degrees or less than 45 degrees relative to thelongitudinal axis of the damper tube 48. In one preferred arrangement,the angle is approximately 45 degrees relative to the longitudinal axisof the damper tube 48. In addition, the tube portion 46 a preferably hasa maximum width (dimension in a direction generally perpendicular to aline connecting the centers of the openings at the end portions) that isless than the diameter of the interior space of the air sleeve 50. Thus,the air sleeve 50 preferably can pass partially or completely over thetube portion 46 a. One or more of the exit angle, shape or size of thetube portion 46 a assists in permitting the air sleeve 50 to passpartially or completely over the tube portion 46 a of the tube assembly46.

Preferably, the air sleeve 50 can pass over the tube portion 46 a asufficient distance such that the seal 90 of the air spring piston 56 isexposed or accessible. In at least one arrangement, the air sleeve 50can pass over the tube portion 46 a a sufficient distance such that theseal 70 passes beyond the closed end 60 of the damper tube 48. In atleast one arrangement, the air sleeve 50 can pass completely over thetube portion 46 a. If necessary or desired, new seals (e.g., seals 70and/or 90) can be passed over reservoir body portion 44 or over the endcap 52 and assembled to the air sleeve 50 or piston 56, respectively. Insome arrangements, the end cap 52 may be removable from the piston rod78, without releasing damping fluid from the damper, and the replacementseals can be passed over the piston rod 78 and assembled to the airsleeve 50 or piston 56.

As the accompanying figures show, the rear shock 38 has other featuresand components such as seals which will are shown but not describedherein that are obvious to one of ordinary skill in the art.Accordingly, a discussion of these features has been omitted.

Although the present invention has been explained in the context ofseveral preferred embodiments, minor modifications and rearrangements ofthe illustrated embodiments may be made without departing from the scopeof the invention. For example, but without limitation, although thepreferred embodiments described the bicycle damper for altering the rateof compression damping, the principles taught may also be utilized indamper embodiments for altering rebound damping, or for responding tolateral acceleration forces, rather than vertical acceleration forces.In addition, although the preferred embodiments were described in thecontext of an off-road bicycle application, the present damper may bemodified for use in a variety of vehicles, or in non-vehicularapplications where dampers may be utilized. Furthermore, the pressureand flow equalization features of the inertia valve components may beapplied to other types of valves, which may be actuated by accelerationforces or by means other than acceleration forces. Accordingly, thescope of the present invention is to be defined only by the appendedclaims.

What is claimed is:
 1. A bicycle rear shock absorber, comprising: adamper tube that defines a first diameter; a piston rod that defines asecond diameter, where said piston rod carries a piston, said piston andsaid piston rod capable of telescopic movement with respect to saiddamper tube, wherein said piston cooperates with said damper tube to atleast partially define a variable volume compression chamber and atleast partially define a variable volume rebound chamber; a reservoirtube that is separate and remote from said damper tube, wherein saidreservoir tube defines a reservoir chamber of said shock absorber,wherein fluid is displaced to said reservoir chamber from saidcompression chamber during compression movement of said shock absorber,and wherein fluid returns to said compression chamber from saidreservoir chamber during rebound movement of said shock absorber;wherein a ratio of said first diameter to said second diameter isbetween about 1.05:1 and about 1.75:1, and wherein approximately 50% ormore of compression damping during said compression movement of saidshock absorber is accomplished by a compression damping circuit locatedin said reservoir tube, said compression damping circuit comprising apressure-activated valve and an acceleration-activated valve, saidacceleration-activated valve comprising an inertia mass slidablysupported on a shaft, wherein a compression fluid flow of damping fluid,generated by compression movement of said piston and said piston rodrelative to said damper tube, can pass through and be regulated by saidpressure-activated valve without passing through said shaft.
 2. Thebicycle rear shock absorber of claim 1, wherein said ratio is about oneof the following ratios: 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1 and1.7:1.
 3. The bicycle rear shock absorber of claim 1, wherein said ratiois about 1.48:1.
 4. The bicycle rear shock absorber of claim 1, whereinthe second diameter is between about 6-20 mm.
 5. The bicycle rear shockabsorber of claim 1, wherein the second diameter is about 12 mm.
 6. Thebicycle rear shock absorber of claim 1, wherein approximately 50, 60,70, 80 or 90% or more of said rebound damping is accomplished by arebound damping circuit located in said damper tube.
 7. The bicycle rearshock absorber of claim 1, further comprising a bleed valve, whereinsaid flow of damping fluid that passes through said bleed valve alsopasses through said shaft.
 8. The bicycle rear shock absorber of claim1, wherein said pressure-activated valve separates said reservoirchamber from said compression chamber.
 9. The bicycle rear shockabsorber of claim 1, wherein the first diameter is between about 8-35mm.
 10. The bicycle rear shock absorber of claim 9, wherein the seconddiameter is between about 6-20 mm.
 11. The bicycle rear shock absorberof claim 9, wherein the first diameter is about 17.7 mm.
 12. The bicyclerear shock absorber of claim 11, wherein the second diameter is about 12mm.
 13. The bicycle rear shock absorber of claim 1, wherein a differencebetween the first diameter and the second diameter is between about 1.5mm and about 9.5 mm.
 14. The bicycle rear shock absorber of claim 13,wherein said difference is between about 1.5 mm and about 8 mm.
 15. Thebicycle rear shock absorber of claim 13, wherein said difference isabout one of the following differences: 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7mm, 8 mm and 9 mm.
 16. The bicycle rear shock absorber of claim 13,wherein said difference is about 1.5 mm.
 17. The bicycle rear shockabsorber of claim 1, wherein approximately 70, 80 or 90% or more of saidcompression damping is accomplished by said compression damping circuitlocated in said reservoir tube.
 18. The bicycle rear shock absorber ofclaim 17, wherein approximately 50, 60, 70, 80 or 90% or more of saidrebound damping is accomplished by a rebound damping circuit located insaid damper tube.
 19. The bicycle rear shock absorber of claim 1,wherein at least 30% of the damping fluid within said damper tube isdisplaced to said reservoir chamber during a complete compressionstroke; and wherein said compression damping circuit comprises anexternally-accessible adjustment mechanism located on the reservoir tubethat permits adjustment of a damping rate of said compression dampingcircuit by varying a regulation of a compression fluid flow of dampingfluid, which is generated by compression movement of said piston andsaid piston rod relative to said damper tube.
 20. The shock absorber ofclaim 19, wherein at least about 40, 45, 50, 60, 70, 80 or 90% of thedamping fluid within said damper tube is displaced to said reservoirchamber during a complete compression stroke.
 21. The shock absorber ofclaim 19, wherein about 46% of the damping fluid within said damper tubeis displaced to said reservoir chamber during a complete compressionstroke.
 22. The bicycle rear shock absorber of claim 19, whereinapproximately 50, 60, 70, 80 or 90% or more of said rebound damping isaccomplished by a rebound damping circuit located in said damper tube.23. The bicycle rear shock absorber of claim 19, wherein approximately70, 80 or 90% or more of said compression damping is accomplished bysaid compression damping circuit located in said reservoir tube.
 24. Thebicycle rear shock absorber of claim 23, wherein approximately 50, 60,70, 80 or 90% or more of said rebound damping is accomplished by arebound damping circuit located in said damper tube.
 25. The bicyclerear shock absorber of claim 19, wherein fluid from said compressionchamber enters said reservoir chamber at a first end of said reservoirtube, and wherein said adjustment mechanism is located at said first endof said reservoir tube.
 26. The bicycle rear shock absorber of claim 25,wherein said compression damping circuit comprises a bleed valve, andwherein said adjustment mechanism permits adjustment of said bleedvalve.
 27. A bicycle rear shock absorber, comprising: a damper tube thatdefines a first diameter; a piston rod that defines a second diameter,where said piston rod carries a piston, said piston and said piston rodcapable of telescopic movement with respect to said damper tube, whereinsaid piston cooperates with said damper tube to at least partiallydefine a variable volume compression chamber and at least partiallydefine a variable volume rebound chamber; a reservoir tube that isseparate and remote from said damper tube, wherein said reservoir tubedefines a reservoir chamber of said shock absorber, wherein fluid isdisplaced to said reservoir chamber from said compression chamber duringcompression movement of said shock absorber, and wherein fluid returnsto said compression chamber from said reservoir chamber during reboundmovement of said shock absorber; wherein said second diameter is betweenabout 8 mm and about 14 mm; wherein a ratio of said first diameter tosaid second diameter is between about 1.05:1 and about 2.5:1; andwherein compression damping during said compression movement of saidshock absorber primarily occurs in a compression damping circuit locatedin said reservoir tube, said compression damping circuit comprising anacceleration-activated valve comprising an inertia mass slidablysupported by a shaft, wherein said shaft has a free end and an endsupported by said reservoir tube, wherein said inertia mass is normallybiased away from said free end of said shaft.
 28. The bicycle rear shockabsorber of claim 27, wherein said ratio is between about 1.05:1 andabout 2:1.
 29. The bicycle rear shock absorber of claim 27, whereinrebound damping during said rebound movement of said shock absorberprimarily occurs in a rebound damping circuit located in said dampertube.
 30. The bicycle rear shock absorber of claim 27, wherein saidcompression damping circuit further comprises a pressure-activatedvalve, wherein a flow of damping fluid can pass through saidpressure-activated valve without passing through said shaft.
 31. Thebicycle rear shock absorber of claim 30, further comprising a bleedvalve, wherein said flow of damping fluid that passes through said bleedvalve also passes through said shaft.
 32. The bicycle rear shockabsorber of claim 31, wherein said bleed valve is located within aninterior passage of said shaft.
 33. The bicycle rear shock absorber ofclaim 31, further comprising an externally-accessible adjustmentmechanism that permits adjustment of a damping rate of said bleed valve.34. A bicycle rear shock absorber, comprising: a damper tube thatdefines a first diameter; a piston rod that defines a second diameter,where said piston rod carries a piston, said piston and said piston rodcapable of telescopic movement with respect to said damper tube, whereinsaid piston cooperates with said damper tube to at least partiallydefine a variable volume compression chamber and at least partiallydefine a variable volume rebound chamber; a reservoir tube that isseparate and remote from said damper tube, wherein said reservoir tubedefines a reservoir chamber of said shock absorber, wherein fluid isdisplaced to said reservoir chamber from said compression chamber duringcompression movement of said shock absorber, and wherein fluid returnsto said compression chamber from said reservoir chamber during reboundmovement of said shock absorber; wherein a ratio of said first diameterto said second diameter is between about 1.05:1 and about 1.75:1, andwherein approximately 50% or more of compression damping during saidcompression movement of said shock absorber is accomplished by acompression damping circuit located in said reservoir tube, saidcompression damping circuit comprising a pressure-activated valve and anacceleration-activated valve, said acceleration-activated valvecomprising an inertia mass slidably supported on a shaft, wherein a flowof damping fluid can pass through said pressure-activated valve withoutpassing through said shaft; a bleed valve, wherein said flow of dampingfluid that passes through said bleed valve also passes through saidshaft and wherein said bleed valve is located within an interior passageof said shaft.